lots of wheelz with russian airliners

Thanks for that, I always wondered what those things were trying to do on the Citation!

Looking into this some more, I can’t seem to find anything regarding use of the “thrust attenuators” (that’s what they’re called it turns out) on landing for the CitationJet. My original information regarding thrust attenuators came from a USAF T-37 Tweet instructor which has a similar set up to the CitationJet. What I explained before regarding the use of the attentuators during landing to permit a higher rpm for a possible go-around was a procedure on the T-37 (as explained by him) but it was his belief that it was the same for the CitationJet.

They are an airplane oddity for sure. Anyone else know something about these?

Originally posted by wysiwyg
A further interesting bit of info – on the 757 (and presumably all jets with underslung wing engines) we only use reverse idle until the nosewheel is on the ground to avoid the reverse thrust rapidly pitching the aircraft nose down and damaging the nose gear.

The reverse is true for rear mounted engines. It’s advisable to avoid reverse thrust before the nose is on the ground as it will raise the nose since the thrust vector is aft of the main gear. As I stated before, the first versions of the ERJ had logic to prevent anything other than idle thrust with the reverser deployed until the nose was on the ground. It seems at some point that logic was altered as I talked to several pilots who were alarmed to find the nose rising on them in the touchdown after they deployed the buckets. Embraer did change the logic on us with no one knowing about it.

Originally posted by Interflug62M
I was told by a Cubana IL62M Capt. that the two reasons for pre-touchdown thrust reverser deployment on the 62 was to enable faster “spool up” time in case of a go around situation

This could very well be. I know the Cessna CitationJet (525/CJ1/CJ2) have small centrifugal flow engines that are slow to spool compared to their axial flow counterparts. For this reason they are equiped with exhaust deflectors (I don’t know the actual name) that are used on approach/landing. With the defectors deployed the engines can be kept at a higher RPM. If a go around situation is encountered the defectors are retracted, requiring less time to achieve GA thrust. Here’s a picture. You can see the deflector aft of the engine.

http://www.airliners.net/open.file/422922/M/

Looking at the ILM 62 picture, the reversers aren’t fully deployed which leaves acting as the deflectors on the CitationJet do. I just assumed they were in transition to full reverse in the picture which would be a bad thing.

Apologies for the lateness of this reply but I have been away on holiday, followed by a busy work pattern and a tax return to complete!

Matthew – your synopsis is generally correct but perhaps I can expand a bit on how the 757 system works. The 757 has 2 ground to air switch systems for signalling to different things. The reverse thrust system (and some other systems) have a sensor in the tilt mechanism on the main gear bogies. As soon as the bogies start to tilt on touchdown the thrust reverse system becomes available (as long as the thrust levers are moved to idle). Other systems (such as the stall warning and warning and caution systems) use a logic switch on the compression of the nose gear leg. This was the problem on the MYT 757 in Mahon the other month.

A further interesting bit of info – on the 757 (and presumably all jets with underslung wing engines) we only use reverse idle until the nosewheel is on the ground to avoid the reverse thrust rapidly pitching the aircraft nose down and damaging the nose gear. For a similar reason, any autobrake setting higher than setting 1 will not cut in until the body angle has lowered to +1 degree relative to the horizon.

RobC – Reverse thrust does indeed improve landing performance however when performance is being calculated reverse thrust is not taken into consideration (i.e. it is assumed to be unserviceable). Interestingly enough in the event of an engine failure it is still possible to use full reverse thrust on the remaining engine during thed landing roll commensurate with maintaining directional control.

regards
wys

I was told by a Cubana IL62M Capt. that the two reasons for pre-touchdown thrust reverser deployment on the 62 was to enable faster “spool up” time in case of a go around situation and to compensate for the IL62s absence of leading edge devices which on comparable “Western” types permit a lower landing speed and thus a reduced landing distance

Re: lots of wheelz with russian airliners

Originally posted by Jeanske_SN
hi i noted that russian airliners have more wheels than western. do they think it’s cool (it is actually, look at the tu 144). the tu 154 has the number of wheels like the 777 but it maybe wheigs half. and the tu 204 is an a321 but it has wheels like the 757.

Hi Jeanske,

Wysiswyg and Theplane are right! I remember reading an interview with the main designer of the Tu124 he was asked “why he designed the main gear that heavy and rugged as it does not have a good effect on the descent?” he answered: “Do you think i’m crazy? I know very well that the landing is not affected positively, but in the harsh winters of Siberia and unpaved strips could damaged a landing gear beyond repair” ……i was so impressed by this that i never forgot this quote and it was some 10-15 years ago that i read it. It is true that the more wheels the better the weight is distributed and does not press as much on the strip or taxiway. This means a much better handling on the ground especially on unpaved runways as the plane does not sink in the mud or sink in the ground.
The larger western aircrafts also use this principle see B747, A340, DC10/MD11, Galaxy C5 or the newly C17.

IO hope this helps 😀

agreed…most Russian aircrafts are equiped for operating on gravel airstrips……. hence the more numbers of wheels.

on the Tu154 picture only the no1 & no3 engine have reversers deployed as (i think) the no2 does not have one.

On the DC8 it was allowed to put the inboards (only) into reverse in flight to increase the rate of plummett 🙂

Originally posted by tenthije
All I know is that it is not necessary for both the main and the nose gear to be on the ground for the trust reversers to be deployed. I have seen this on many planes including the A340 (pic), B767, B737 and more.

Most aircraft will allow you to “pop the buckets” and even spool them up when you have weight on the main wheels. I know the earlier models of the EMB145 aircraft won’t let you spool the engines up unless the nose is on the ground.

That Russian aircraft has no weight on any of the wheels. Perhaps it run through the Radio Altimeter? At 100 feet you can deploy the buckets. 🙂 As wysiwyg said, it’s a sure way to have a rapid decent.

Shouldnt that increase landing performance, by being able to land at shorter runways, but then again they have to take off too 🙂

All I know is that it is not necessary for both the main and the nose gear to be on the ground for the trust reversers to be deployed. I have seen this on many planes including the A340 (pic), B767, B737 and more.

I would not be surprised if the reverser on the A340 pictured was already deployed when you see the pic. Just look at the angle of attack!

http://www.jetphotos.net/viewphoto.php?id=121526

Well not only do Russian liners have more wheels they have more cockpit windows, i always think of them as a more of a spaceship 🙂

Well spotted WD, I hadn’t noticed. On Boeings the reversers are locked closed until touchdown and presumably the same is true with Airbus. The only western aicraft I know hat was allowed to use reverse in flight was the Trident although I think it may be possible in the DC8 as well. Even so I wouldn’t want to use it in the flare as it would make you fall out of the sky.

That aircraft is landing with the thrust reversers deployed. Isn’t that called an emergency on other aircraft?

ok…….wys answered it better than i could…;)

hey jeanske….
i think it has more to do with the russian airliners being built to operate from unpaved airstrips… but maybe someone else can enlighten us…

A lot of Russian aircraft are designed to operate from rather unprepared airstrips so their designers allow many tyres for good load spreading ability. It also allows reasonable back up in the event of tyre failure.